Field of the Invention
The present invention relates to an image capturing apparatus, image capturing system, and a control method for the image capturing apparatus.
Description of the Related Art
The number of pixels that can be recorded in image capturing apparatuses such as digital video cameras has increased in recent years. This is closely related to the standards of monitors for displaying video recorded by image capturing apparatuses. Specifically, there has been a transition from the so-called SD (Standard Definition) standard to the so-called HD (High Definition) standard, and a transition to monitors having an even higher resolution is planned for the future.
The HD resolution is mainly 1920 pixels in the horizontal direction by 1080 pixels in the vertical direction (referred to hereinafter as 1920×1080 pixels), and the resolution of so-called 4K2K monitors thought to be the next generation is 3840×2160 pixels, which is four times the number of pixels in the HD standard. Also, the standard being developed for digital cinema is 4096×2160 pixels, which is higher than the number of pixels in the 4K2K standard. Also, the so-called 8K4K standard is thought to be the next generation after the 4K2K standard, and this standard has 7680×4320 pixels. With this standard, the number of pixels for digital cinema would be thought to be over 8K in the horizontal direction.
This change has been accompanied by a requirement for image capturing apparatuses to be able to record a higher number of pixels as well. For example, in order to be compatible with the number of recording pixels in the aforementioned super high-vision, lenses, image sensors, image processing LSIs for performing digital processing on video signals, video output LSIs for externally outputting video signals, and the like need to be compatible with a high number of pixels. The pixel count of image sensors also needs to be compatible with the number of pixels in super high-vision.
In recent years, there have been cases where CMOS image sensors used as image sensors in image capturing apparatuses have generated various types of noise due to their structure. Specific examples of such noise include FPN (Fixed-Pattern Noise) in the vertical direction, vertical line noise caused by sensitivity non-uniformity (PRNU), and noise caused by dark current non-uniformity (DSNU). Normally, FPN correction is performed in real-time in image processing LSIs in image capturing apparatuses and the like. FPN correction is performed using data acquired from an optical black (OB) pixel region of the image sensor.
However, since the amount of information per frame is large in a video signal that has a high pixel count, correcting it in real-time involves a high processing load. This leads to the problems of an increase in the scale of the image processing LSI and an increase in power consumption.
Japanese Patent Laid-Open No. 2007-300282 discloses a system in which image data from an image sensor is recorded as RAW data not subjected to image processing, and then image processing is performed at a later time. Using the technique in Japanese Patent Laid-Open No. 2007-300282, image data can be directly recorded as RAW data without being subjected to correction processing such as FPN correction in real-time, thus making it possible to reduce the processing load during image capturing. Development processing can be performed on the RAW data at a later time without placing a large burden on the image processing LSI.
However, when the technique in Japanese Patent Laid-Open No. 2007-300282 is used, correction processing that uses OB pixel region data, such as FPN correction, is performed at a later time, and therefore output images from the image sensor are recorded as RAW data that includes the OB pixel region as well. For this reason, the RAW data has a large size, and the amount of capacity consumed in the recording medium increases.